Compact heating and cooling system

ABSTRACT

A compact absorption refrigeration unit has a central mounting core containing a generator about which substantially all of the components of the refrigeration system are mounted in a predetermined configuration. The generator has heat transfer fins secured to its surface which have a predetermined configuration that allows the fins and generator to absorb heat at the optimum rate at which heat can be transferred thereto without damage to the fins. The unit also includes an evaporator having a centrally positioned reservoir and a helical passageway providing a flow path for a heat exchange medium and containing a fluted helical heat exchanger tube which provides a countercurrent refrigerant, thereby to chill said heat exchange medium. In one embodiment of the invention the unit is provided with a compact boiler for use in heating the heat exchange medium, thereby permitting the unit to be selectively operated for both heating and cooling.

United States Patent Malcosky et al.

[ 1 Sept. 23, 1975 COMPACT HEATING AND COOLING SYSTEM [75] Inventors: Norman D. Malcosky; Ronald H.

McLean, both of Columbus; Kanwal N. Singh, Westerville; Chung M. Auh, Columbus, all of Ohio [73] Assignee: Columbia Gas System Service Corporation, Wilmington, Del.

[22] Filed: June 28, 1974 [21] Appl. No.: 484,460

Related US. Application Data [62] Division of Ser. No. 350,822, April 13, 1973, Pat.

[52] US. Cl 165/63; 165/146 [51] Int. Cl. F25B 29/00 [58] Field of Search 62/399, 476, 485, 486, 62/489, 495, 496, 497; 165/63, 59, 161, 146, 163, 172

[56] References Cited UNITED STATES PATENTS 2,184,345 12/1939 Hersey 165/172 X 3,223,152 12/1965 Schulenberg 165/146 3,627,031 12/1971 Ware 165/48 X A. Razzano [57] ABSTRACT A compact absorption refrigeration unit has a central mounting core containing a generator about which substantially all of the components of the refrigeration system are mounted in a predetermined configuration. The generator has heat transfer fins secured to its surface which have a predetermined configuration that allows the fins and generator to absorb heat at the optimum rate at which heat can be transferred thereto without damage to the fins, The unit also includes an evaporator having a centrally positioned reservoir and a helical passageway providing a flow path for a heat exchange medium and containing a fluted helical heat exchanger tube which provides a countercurrent refrigerant, thereby to chill said heat exchange medium. In one embodiment of the invention the unit is provided with a compact boiler for use in heating the heat exchange medium, thereby permitting the unit to be selectively operated for both heating and cooling.

14 Claims, 7 Drawing Figures US Patant Sept. 23,1975 Sheet 1 of4 3,907,025

US Patent Sapt. 23,1975 Sheet 3 0M 3,07,

REFRIGERANT CONDENSING UNIT AIR TREATING UNIT III

LIQUID 2 I m I? 4 I f O 4 2 I a 6 h l S m 5 7 q 9 I, 3 2 v m M e S 9 QOI US Patent HEATER time."

' 'CQMP:ACT HEATING AND cooLING SYSTEM l sy st'em which may be selectively operated 'for either cooling or heating the air conditioned space as desired.

There hasrecc ntly'bee'n: an increased demand for air Conditioning heating and cooling units for'use in residential spaceconditioningj In particular the demand hasincre a's'ed for gas fired air conditioning units which are compact in size and quiet in operation while maintaining high standards of performance and reliability and with minimum service'over extended periods 'of In order to limit the amountof space occupied in a home or'residential building by the air'conditioning and heating systems, it has become desirable 'to' produce residential gas air conditioning systems which can also serve as a heating system during the Winter months and thus provide complete space conditioning for residences a' single unit or package. Another feature which is desired in air conditioning systems for homes is that the system be located out of doors, thereby to provide more occupiable space within the residence itself.

" Accordingly, it is an object of the present invention toprovide an economical, inexpensive and reliable air conditioning system for residential use.

Yet another object of the present invention is to'provide space conditioning systems which satisfy the abovementioned demands and desires.

A further object of the presentinvention is to provide efficient and economical components for such systems.

In accordance with an aspect of the present invention, a compact air conditioning system is providcd which includes a central, generally cylindrical hollow core on which substantially all of the components of the air conditioning system are mounted or supported. The core and the air conditioning components are enclosed within a removable frame structure which is not connected'to any of'the air conditioning components, so that the entire air conditioning system and its components can be conveniently exposed for assembly, inspection'and repair. In one illustrative embodiment of thepresent invention; the space conditioning system is used'to cool the interior ofa building, e.g. a residential structure and is located outside of'the building, with only an air distribution plenum system, and a fan/coil heat exchanger unitlocated within the building. In another embodiment, the system can be readily converted to one which will selectively provide both cooling and heating. 1

In one preferred embodiment, the compact space I conditioning system of'the present invention includes a vapor generator assembly which is adapted to receive a strong refrigerant solution which is heated by a gas fired combustion means located below the generator to 'producerefrigera'nt vapor. A heat exchange condenser is'connected in fluid communication with the generator for receiving and condensing the'generated refrigerant vapor, with the cooled refrigerant liquid flowing from the condenser through a refrigerant heat exchanger. The latter is connected in fluid communication with a heat exchange evaporatorQthroughafirst restriction, means, whereby cooled refrigerant liquid issupplied to the evaporator for cooling a heat exchange medium flowing therein."The refrigerant heat exchanger r'eceives refrigerant vapor from theevaporator and passes it countercurrently with the refrigerant liquid flowing from the condenser to the evaporatorgthereby to further cool the refrigerant liquid prior to passage through the first restriction means to the evaporator. In addition, a heat exchange absorberis connected in fluid communication 'with the refrigerant heat exchanger and with a solution heat exchanger. Weak refrigerant solution is supplied from the generator through the solution heat exchanger to the absorber wherein the weak solution absorbs'refrigerant vapor supplied from the evaporator. A second fluid flow restriction means is located between the solution heat exchanger and the absorber for maintaining a pressure differential therebetween. A solution pump is provided for pumping strong refrigerant solution produced. in the absorber and'supplying a first portion thereof directly to a rectifier heat exchanger, and a second portion thereof to the top of the analyzer via a solution heat exchanger, wherein the strong refrigerant solution flows in heat exchange relation to the weak solution. Thus, heat is added to the second portion of the refrigerant solution prior to passage into the generator. In another embodiment of the invention, the air conditioningsystem is provided with l a selectively operable boiler by which the systemis the vapor generator assembly of FIG. 4;

conveniently converted from a tion to a heating mode.

The present invention provides an airconditioning system which is relatively compact in construction, since all of the components thereof are mounted on a single central core, in a close compact relationship to one another, so that the system can be conveniently installed out of doors adjacent the building to be conditioned and in as inconspicuous a location as possible. Accordingly, the air conditioning system does not occupy any valuable floor space within the building;

The above, and other objects, featuresand advantages of this invention, will be apparent in the following detailed description of an illustrative embodiment thereof which is to be read in connection with the'accompanying drawings wherein: I I

FIG. 1 is a perspective view of a space conditioning unit constituting one embodiment of the present inven' tion;

FIG. 2 is a diagrammatic view of the components of the space conditioning unit illustrated in FIG. 1:.

FIG. 3 is a sectionalview, with parts broken away. taken along line 3-3 ofFIG. l; 1

FIG. 4 is an enlarged vertical section of the vapor generator assembly utilized in the space conditioning .unit of the present invention;

FIG. 5" is a plan view of a heat transfer fin utilized i cooling mode of opera FIG. 6is an enlarged sectional-view ofthe evaporator of the unit of FIG. I; and i FIG. 7 is an exploded perspective view of the.compact boiler of the unit of FIG, I.

Referring to FIGS. 1 and 2 of the drawings, it is seen that the space conditioning unit 10 of the present invention, which includes a gas fired absorption refrigeration system and a gas heating-unit, is generally cylindricalwith an outercasing or shell structure 12. Casing 12 includes a lower wall 14 formed of panels of corrugated sheet metal secured to each other by a plurality of screws 16. These panels are mounted upon a base 18 formed by a circular bottom wall 17 and a peripheral flange 19 (FIG. 3) for supporting the various components of the entire air conditioning unit.

The main structural component of the air conditioning unit is a central core 20 (FIG. 3) which is centrally mounted on base 18 and provides an enclosure for the generator assembly and associated components of the unit. Core 20 is formed by lower and upper cylinders 54 and 56 and a frustroconical collar 52 mounting cylinder 56 in vertical axial alignment on cylinder 54. This core provides support for substantially all of the other components of the unit.

Each of a plurality of radially extending arms 22 is secured to core 20 and provides support for an intermediate annular support plate 24. Corrugated panels 14 are secured between base 18 and arms 22 and provide a lower enclosure for various components of the unit. The upper portion of the unit is enclosed by a cylindrical, foraminous casing wall 28 which is formed of perforated sheet metal that defines a large number of relatively uniform openings 29 providing communication between the atmosphere and the interior of the unit, thereby permitting ambient air to flow into and through the upper portion of the unit. Casing wall 28 is supported on and secured to, support plate 24 in any convenient manner. The top of the unit is closed by a lid 34 resting upon a peripheral ring 35 secured to wall 28. Lid 34 has an open wire top 36, which permits ambient air to flow from the top of the unit.

As indicated above, unit 10 includes an absorption type refrigeration system which has a vapor generator assembly 38 enclosed within central core 20. Generator assembly 38 is enclosed within a generally cylindrical pressure vessel to which a strong aqua-ammonia solution is supplied and in which refrigerant vapor is driven from the solution upon heating by a gas burner assembly 40. Burner assembly 40 produces a flame front below the generator assembly 38 within the annular flue passages 48 of the generator assembly. The burner assembly is of the semi-powered blue flame type since combustion air is supplied to the venturi of the burner as a result of the slight vacuum created in the unit by the condenser fan 100, more fully described hereinafter. This fan draws air in the unit and thus supplies air to the burner. which air is 100% premixed with the fuel gas so that no secondary air is required to complete the combustion process. This burner has an extremely short flame height; that reduces the overall height of the unit. Moreover, the air-to-fuel ratio is substantially stochiometric so that a peak flame temperature and a maximum efficiency are obtained.

The combustion products of burner assembly 40 are confined to an annular flue 48 adjacent the outer heat transfer surface 44 of generator assembly 38 up to the level of plate 24 by an insulation liner 46 on the inner surface of cylinder 54 of central core 20. The products of combustion are discharged from flue 48 through apertures 50 in collar 52;

The heat transfer from the products of combustion to the generator is provided by uniquely shaped heat transfer fins 58 (see FIGS. 4 and 5) welded to the lower portion of the heat transfer surface 44. The width of the fins 58 vary along their length l, which length in the preferred embodiment of the present invention is thirteen and one half inches, so that each fin absorbs heat without damage at the same rate at which heat will pass through the fin and the heat exchange wall to the fluid contained therein when the temperature at the edge of the fin is near, but less than the maximum permissible temperature for the fin. By this arrangement, the fins do not have excessively hot spots along their surfaces and the life of the structure is prolonged.

The configuration of the outer edge of each of fins 58 will, in the optimum configuration, conform to a developed curve of predetermined characteristics. However, in the preferred embodiment of the invention, the edge configuration of the fins is formed by straight edge sections of predetermined slopes and the overall effect is an acceptable deviation from the optimum curve. Thus, as shown in FIG. 4, fins 58 are constructed so that the lower portion thereof has a length 1 (preferably 2.4 inches long) along which the fin extends from a minimum width (of 0.5 inches) to a first intermediate width (of 1.50 inches). Along this length of the heat exchanger fins, the combustion product gases are at relatively high temperatures and thus the dimensions of the fins must be small in order to prevent their becoming overheated by contact with those products of combustion. Along the length 1 (preferably 4.5 inches long), fins 58 further expand their width to a maximum width (of 2 inches) at an intermediate point along their length. Along this portion of the lengths of the fin, the products of combustion are channeled between the fins toward surface 44 into the greater fin width, to transfer heat to the generator, without excessive heating of the fins. This is an important feature of the invention since the hotter gases adjacent liner 46 are gradually channeled or directed towards the inner portions of the fins to improve heat transfer without overheating the fins or creating hot spots such as would cause oxidation of the fins. Overheating and/or hot spots in the fins also is undesirable since it will cause breakdown of the refriger ant in the generator.

Finally, along a length 1 (preferably 5.5 inches), the width of the fins is of a uniform dimension of 2 inches, and the edges 60 of the fins abut the surfaces 62 of the insulated liner 46 on the interior of cylinder 54. Accordingly, it is seen that the distance between the edge 60 and the inside surface 62 of insulation 46 steadily decreases to an intermediate point along the lengths of the fins so that the flue gases progressively encounter the edges of the fin and are forced into the passageways formed between the fins. In this manner, as the com-. bustion products between the fins cool and heat transfer drops, the higher temperature combustion products adjacent the outer ends of the fins are forced into and between the passages of the fins so as to maintain relatively uniform heat transfer with the generator. to improve and obtain a more efficient heat transfer between the combustion products and generator 38.

In addition, since fins 58 extend parallel to each other, all of the heat exchanger surfaces are constantly swept by the combustion products. thereby improving heat transfer. Moreover, the construction of the generator, with the annular flue 48 in which fins 58 are located creates a slight pressure differential in the flue under the influence of condenser fan 100. The pressure differential created by condenser fan in this manner acts through the burner to draw ambient air through the venturi of the burner 40, thereby providing 100 percent aeration for the burner to obtain maximum efficiency therewith.

In the preferred embodiment, fins 58 (see FIG. 5) are in pairs, with each pair having a generally channelformed as separate independent plates welded or otherwise secured to the generator.

As mentioned above, a stream of strong aquaammonia solution is supplied to the generator assembly in order to produce refrigerant vapor and weak refrigerant solution. The refrigerant vapor produced in the generator moves upwardly towards the top of the generator assembly for use in the air conditioning system, as described hereinafter, while a weak solution at an acceptable level remains in the generator. This level generally extends to a position adjacent the top of an analyzer assembly 70 contained within the generator; and preferably to the level of a refrigerant check tube 69 extending from the generator wall 38.

The weak solution flows from the generator, due to the pressure therein (as described more fully hereinafter) through a heat exchanger tube 68 of the analyzer assembly 70 contained within the generator. Tube 68 is a helix of a diameter so that it is spaced from the inner surface of vessel 38 and extends axially from the bottom of the generator assembly upwardly above the level of plate 24. (It is noted that in FIG. 4 of the drawing, the central portion of the tube 68 has been broken away for clarity.)

Coaxial with tube 68 is the analyzer assembly 70, formed by a central mounting post 71 supported on the bottom wall 42 of vessel 38. This mounting post has a hollow lower end portion which receives the curved lower end 73 of tube 68. By this construction the opened end 73 is directed away from the bottom of the generator and does not pick up, with the weak'solution, any sediment lying on the generator bottom.

A series of mass transfer baffle plates 72 are mounted on post 71, with each of the plates being slightly more than one-half of a disk having the radius of the inner surface of vessel38. The plates are mounted upon post 71 in alternated right and left relationship, as shown. Hence, one plate forms a baffle from one side of the vessel to beyond the post toward the opposite side, and each of the adjacent baffles form similar baffles from that opposite side beyond the post toward that one side. This construction forms a liquid-vapor counterflow relationship between the liquid flowing downwardly back-and-forth from plate to plate, and with vapor flowing upwardly.

Cool strong solution is supplied to the generator (as described hereinafter) and flows downwardly under the influence of gravity. This cooled solution passes over plates 72, and over the windings of the heat exchanger tube 68, so that it exchanges heat with the hot weak so lution flowing in tube 68. As a result, additional heat is supplied to the strong solution, thereby to produce vaporization of the refrigerant vapor therein, and the weak solution leaves the analyzer highly subcooled through an outlet 74 in tube 68.

From outlet 74 the weak solution passes through an external solution heat exchanger 76 where further cooling of the weak solution takes place. The solution heat exchanger comprises a helically wound tubewithin-a-tube assembly located concentrically around the upper portion 78 of vessel 38, between the exterior wall of the vessel and the upper portion 56 of center core (see FIG. 3).

Solution heat exchanger 76 is used to transfer heat between the weak solution from the generator and a portion of the strong solution returning to the generator from the absorber. The weak solution flows through the inner tube80 of the heat exchanger. This tube extendsinto and through a large diameter outer tube 82, through which the strong solution flows with the weak solution and strong solution flowing countercurrently to each other in their respective tubes.

Solution heat exchanger 76' increases the thermal efficiency of the operating cycle of the air conditioning ,nia vapor out of the refrigerant solution in the generator.

The weak solution, which is now highly subcooled by passage through solution heat exchanger 76, passes from the heat exchanger through a restrictor 84, i.e. a capillary tube, to the low pressure side of the system. After passing restrictor 84 the weak solution enters an absorber 99 wherein the weak solution absorbs refrigerant vapor prior to return to the generator.

The refrigerant vapor from generator 38, which rises toward the top of the generator contains water vapor which must be removed from the refrigerant vapor. A portion of this water vapor is removed in the analyzer section of the generator wherein analyzer plates 72 function to provide maximum mass transfer contact between the countercurrent liquid and vapor streams so that the aqua-ammonia vapor directly contacts the cooler strong solution returning to the generator to cause condensation of some of the water vapor in the stream and vaporization of some of the ammonia in the strong solution droplets. Further purification takes place in the rectifier portion 75 of generator 38. Rectifier 75 is located in vessel 38 directly above the analy zer section and includes a tubular heat exchanger 86 which is helically wound around a closed hollow cylindrical core 86'. A portion of the strong solution flows downwardly to the analyzer through tubular heat exchanger 86 and cools refrigerant gas vapor rising from the analyzer to cause further condensation of water vapor from the gas. The hollow cylindrical core 86' within heat exchanger 86 serves to prevent the refrigerant gas vapor from flowing through the center of the heat exchanger and thus forces the vapor across the outer surfaces of the heat exchanger, to improve condensation. The water condensate from the refrigerant vapor stream drips downwardly on the outside of the rectifier heat exchanger 86 to the lower portion of the generator assembly thereby to form a portion of the weak solution.

In addition, the rectifier portion of the generator assembly includes a Raschig ring bed 92 at the lower section ofthe rectifier heat exchanger 86 wherein the con- .densate formed in the rectifier on the surface of the :heat exchanger86 is refluxed prior to passage into the analyzer section. of the generator, 1 i

The heat of condensation of the water'vapor in the rectifier raises the temperature of thcstrong solution supplied through heat exchanger 86, thereby further reducing the requirement for -heat.from burner 40. The

strong solution flows from the end 88-of heat exchanger 86 through a plurality of apertures 90 onto the top plate of the analyzer section of the generator. This strong 's'olution combines with the other portion ofthe strong solution flowing from the solution heat exchanger and passes-through analyzer 70, exchanging heat and-mass with the countercur-rent vaporstream. and exchanging heat with the-weak solution in the analyzerheat'exchanger 68'. i

' The substantially pure ammonia refrigerant vapor at 'the top 94 of pressure vessel 38 leaves the vessel under pressurethrough conduit'96 and enters the condenser 98 wherein'the vapor is cooled and condensed. Itis noted that both the condenser '98 and absorber 99 are formed as finned, helically wound heat exchanger coils. These coils are located'about the periphery of center core 20 and are" positioned in adjacent and superimpo'scd relationship to one another, as seen in FIGS. 2

and 3. (For convenience, the fins of the condenser 98 havebeen shown in FIGS. 2 and 3 with cross-hatched shading, iwhereas those of the absorber 99 have been left clear.) The 'heat transfer coils of the absorber and condenser are supported on the central platform 24 which, in turn, is seated on and secured to the radially extending ribs 22 secured to core 20. In this manner, the arrangement ofthe components of the conditioning system are made as compact as possible.

In this configuration, both the absorber and the con- ;den ser are exposed to ambient air flowing through cxterior grid 28. In order to draw this ambient air through grid 28, a fan 100 is mounted at the top of central core 20,,and is driven through a belt and pulley arrangement 102, as schematically illustrated in FIG. 3 of the drawing. from a motor-pump 104, as more fully described hereinafter. V

After an initial rapid drop in the temperature of the ammonia refrigerant vapor in the condenser, most of the refrigerant vapor is condensated in the condenser atessentially constant temperature (under the influence of air drawn thereover by fan 100); with the liquid refrigerant leaving the condenser-slightly subcooled. From the condenser 98 the liquid refrigerant is passed .througha conduit 106 ,toa refrigerant heat exchanger 108 in which theliquid refrigerant exchanges heat with cooler counterflowing two. phase refrigerantimixture leaving the evaporator 110 of the air conditioning sys- Conduit, 106, includes a cutrestrictor 107 positioned therein: between the. condenser .98 and therefrigcrant heat exchanger 108; This restrictor serves to maintain therefrigerant in the condenser at an elevated temper- 'atureand prcssure", thereby to obtain improved heat I quired for the condenser. Typically, the restrictor produces a 20 psi pressure drop between the condenser and heat'exchanger 108: In additions-the restrictor 5 causes'some' flashingof the refrigerant it passes therethrough-so that a mixture of vaporl and liquid flows into heat exchanger'lOS. In the latter the refrigerant vapor is recondensed andthus further improves the heat exchange taking place therein.- Refrigerant heat exchanger 108 also constitutesa helically wound tube-within-a-tube heat exchanger (of I 5 .the type described-with respect to the solution heat exchanger) in whichatheliq'uid refrigerant from the condenser passes through afirst or outer tube 112 andis cooled by the coolerrefrigerant returning from evaporator 110 within an inner tube 114. By thus further cooling the liquid refrigerant passing to the evaporator 1 10, the thermal efficiency of the entire air conditioning system is further increased. The refrigerant heat exchanger also is supported on the intermediate support pan 24 (FIG.;3 so as to provide as compact a configuration as possible. The now highly subcooled liquid refrigerant is then passed through an outlet conduit. 116 to an expansion ,valve or capillary tube 118, wherein the subcooled liquid is throttled'at constant enthalpy fromthe highpressure side (condenser) of thesystem to the low pressure side (evaporator) of the sysaem.;Typically, the throttling process through the restrictor causes a small fraction, ,usually-lessthan 10 percent of theliquid, to fhash into a :vapor within the restrictor itself, thereby further reducing the, temperature of the refrigerant.

Evaporator 110 is the structure in which the heat exchange medium-that is to be chilled by space condi- -tioner l0 ispassed. Typically, the heat exchange medium is supplied to the heat exchanger unit of an air/- coil system in whichtambient air is blown over a heat exchanger coil within the home, cooled (or heated) thereby. and supplied through a plenum or duct work systemthroughout the various rooms of the house. In the preferred embodiment of the invention the heat exchange medium used in the evaporator 110 is an ethylene glycol'solution, which will not freeze during the winter months. 7

As illustrated in FIG. 6 of the drawing, evaporator 110 comprises an. outer cylindrical vessel 120 which hasa vertical axis. and contains an inner cylindrical sump tank 122. .Tank 122 has an aperture 124 at its bottom which provides communication with an annular space 126 formed between thev tank'and vessel 120. The latter is covered by an insulation layer 128, and is mounted onbase 18 adjacent core 20, below the condenser and absorber. A spiral vane or baffle 130 is secured to the periphery of tank 122 and has a width equal to the width of the annular, space l26-so that the baffle forms a closed spiraliheat exchange conduit or passage .134.

Heat exchange medium returning -.from the air coil unit in the house is supplied through an inlet port 132 to the uppermost portion of the spiral. conduit 134. As a result. the'heat exchange medium is forced to flow downwardly along the spiral path ofconduit 134 to the base of evaporator ll0,whcrein it isdischarged through a conduit 136 for supply to the-air/coil unit. Conduit -l36 is connectcdin any convenientmanner to a suitable pump 138, whichcauscs the heat exchange medium to flow to-and from the air/coil unit in the house.

Evaporator 1 10 has a top opening 139 through which capillary tube 118 extends downwardly through the center of tank 122. The liquid refrigerant from the refrigerant heat exchanger 112 passes through capillary I tube ll8,'and the interior of core 122, to the inlet end portion 142 of the evaporator hcatiexchanger tube 144. This tube, inthe preferred embodiment of the present invention, comprises a one inch diameter aluminum fluted tube which is spirally wound and. extends through the spiral conduit 134 to the upper portion of the heat'exchanger so that the cold two phase refrigerant mixture passing from capillary tube 118 passes countercurrently through the evaporator; with the heat exchangeme'dium', thereby to'chill the heat exchange medium during the air conditioning mode of operation of the device. in order to provide improved air conditioning operation, fluted tube 144 has a generally square cross-section, as seen most clearly'in FIG. 6, and is twisted about its longitudinal axis so as to form a spiral configuration throughout its entire length. This spi- "ral configuration improves the contact of the heat exchange medium with the surface of the tube 144 as the heat exchange medium' flows through conduit 134,

conduit 134. i

' It is noted that capillary tube 118 passes through the aperture 124 formed in the lower portion of core 122 for connection to the end 142 of tube 144. As mentio ned, this aperture serves to provide liquid communication between the interior of the tank 122 and annular space 126 (and thus conduit 134), whereby the center of tank 122 acts as a reservoir for extra chilled heat exchange medium. Moreover, as described hereinafter, during the heating modeof operation of the conditioning system of the present invention,'this chamber (i.e. the interior of tank 122) acts as an expansion chamber for the heat exchange'medium.

An additiona1 conduit 136 is connected to evaporator 110 and extends therethrough into interior tank 122. The right end of this tube is connected, outside of the evaporator; to a plastic tube or the like (not shown) by which the liquid level in the tank 122 can be checked. That is, by holding the plastic tube vertically, the tank 122, conduit 137 and the" plastic tube act as a manometer. Of course, the plastic tube may be provided with a pinch valve or the like to prevent discharge of fluid from tank 122.

From evaporator 110, the two phase refrigerant mixture passes through conduit 140to the inlet side of tube 114 in refrigerant heat exchanger 108, wherein it serves to cool refrigerant flowing in tube 112 from condenser 98. From tube 114, the two phase refrigerant mixture flows through a conduit 142 to absorber 99. As the two phase refrigerant mixture enters absorber 99, it is mixed with the weak solution flowing through capillary tube 84 from generator 38 and solution heat exchanger76. As a result, the weak solution absorbs refrigerant vapor in the two phase refrigerant mixture. The heat released :by the absorption process taking place in absorber 99 is discharged or rejected from the absorber by'the ambient air which is drawn over the ab sorber by fan 100, and thus is rejected into-the atmosphere.

From absorber 99, the now strong solution refriger ant liquid is passed through a purge pot or reservoir 145 to pump 104. The latter is mounted on the outer surface of the upper portion 56 of center core and is constructed in accordance with the hermetically sealed pump shown and described in US. Pat. Application Ser. No. 313,756, filed Dee-ll, 1972, (Curtis, Morris & Saffords File No. 17-1615),-the disclosure of which is incorporated herein by reference. Pump 104 draws solution from absorber 99, increases its pressure and discharges the strong liquid refrigerant solution along two lines 87 and 148. r Conduit 87 supplies a first portion of the strong solution directly to the rectifier heat exchanger in'the upper portion of the generator, wherein the solution is heated by the condensation of water vapor on the outer portion of tube 86 and by the passage of refrigerant vapor upwardly to the top of the generator. Line 148, on the other hand, supplies a second portion of the strong so lution to the outer tube of'solution heat exchanger 76, wherein it passes in countercurrent heat exchange relation with weak solution flowing from generator 38, through conduit 74, thereby to further increase the temperature of the strong solution and decrease the temperature of the weak solution passing to the absorber. The strong solution passes from the solution heat exchanger through conduit 150, wherein the solution is supplied through a plurality of apertures 152 in the free end 154 of conduit 150 directly above the uppermost analyzer plate 72 of analyzer 70. I

Accordingly, the refrigeration cycle is completed. As thus described, the space conditioning system of the present invention is adapted to be used as a highly efficient air conditioning system for cooling the interior of a home or the like. In onepreferred embodiment of the present invention the system is constructed to produce 36,000 BTUs per hour of cooling capacity. The cooling system operating in this mode has proved to be highly satisfactory, efficient, quiet and to have an extended useful life, over and above that of thepreviously proposed systems. Moreover, because of the compact construction of the air conditioning system, with substantially all of the components mounted on or otherwise supported by the central core member 20 in a predetermined planned configuration, a compact assembly is provided in which each of thecomponents is independent of the exterior framework of the system. Thus, the components are readily accessible for repair and the exterior shell of the system can be conveniently re? moved without damage or movement of the interior parts. Still further, the system is substantially smaller than previously proposed absorption air conditioning systems and thus would be unobtrusive when located outside of the home. In one embodiment of the: present invention the above-identified space conditioning system is adapted to be used as a heating system during the winter months. In this embodiment of the invention the system isprovided with a compact water boiler 160, located downstream of the heat exchange, medium pump 138. This boiler is located within theshell 10 of the space conditioning system and is mounted on center core 20, or otherwise secured to or supported in the lower pan 18 of the system. a 1n the heating mode of operation of the invention, burner 40 is not in operation and the air conditioning components are inactive. Thus, the heat exchange medium flowing between the evaporator and the air/- coil unit in the residence, simply flows into evaporator 1l0 through inlet 132, through spiral conduit 134, and

is discharged through the conduit 136 to pump 138. The latter supplies the heat exchange medium to boiler 160, wherein the heat exchange medium is heated to the desired temperature and supplied through conduit 162 to the air/coil unit within the house.

On the other hand, in the air conditioning mode of operation, the heat exchange medium will also flow through boiler 160, as illustrated in FIG. 2 of the drawing. However, the boiler will be inoperative (i.c. shut off) but heat exchange medium will flow through the heat transfer coil within the boiler. By the novel and unique construction of boiler 160 the temperature of the chilled heat exchange medium flowing through the boiler is not substantially effected as it passes therethrough.

Boiler 160 is more clearly illustrated in FIG. 7 of the drawing; as seen therein, the boiler includes a powered air blower 164 for pressurizing ambient air and supplying the same with gas to the burner I66. The combustion blower 164 mixes the gas supplied from a gas supply line (not shown) with the required amount of air and forces the mixture through a flame holder screen 168. The flame holder preferably is formed of a mesh lnconel wire screen located above a plenum chamber 170 in which there is located an antiflashback wire screen, adjacent the outlet 172 of the combustion blower. Preferably, flame holder 168 has a size of 6 inches by 3 inches, and is located directly below a series of copper finned heat transfer tubes 174.

Heat transfer tubes 174 are arranged in a stacked configuration, with the lowermost tubes 174a in fluid communication with a header 176 to which the heat exchange medium is supplied from pump 138. The heat exchange medium flows through the lowermost tubes 174a, thence through a manifold (not shown), upwardly to the heat exchange tubes 17412 and across the flame holder 168 in an opposite direction; thence through U tubes 178 to the uppermost tubes 1740," and thence through an outlet discharger head 180 to the conduit 162.

In a preferred embodiment of the invention, the fins on the lowermost pair of tubes 174:! have an external diameter which is less than the diameter of the fins on tubes I741). The fins on the latter tubes, in turn, have a smaller diameter than the fins on the tubes 1740. This is done because the products of combustion encounter tubes 174a before tubes 1741) and in turn before tubes 1740. Since the temperature of the products of combustion is higher when they encounter tubes 1740, the smaller fins are used to transfer less heat to the tubes and the heat exchange medium contained therein, thereby preventing damage to the fins on the lowermost tube, while also preventing any thermal degradation by overheating of the heat exchange medium flowing within the tubes.

Preferably boiler 160 is provided with slotted baffle plates I88, 189 between the pairs of tubes 174, as illustrated in FIG. 7 of the drawing. These baffles serve to divert the products of combustion around the entire periphery of each of the heat transfer tubes to provide better contact therebetween and thus better efficiency in transfer of heat from the products of combustion to the heat exchange medium passing through the tubes.

The burner portion 166 of boiler 160 is covered by a shroud 182, of sheet metal construction, having combustion products exhaust 184 which completely encloses the burner portion of the boiler so as to insure efficient contact of the combustion products with heat exchanger tubes 174. Preferably the boiler construction is mounted on a frame 185 which is in turn secured by welding or the like through a bracket 186 to the center core 20 of the space conditioning system. It is also noted that the exterior walls 187 of the boiler are preferably insulated with a high temperature insulating material 190 to insure that substantially all of the heat of the products of combustion is transferred to the heat exchange medium and is not lost through the walls of the boiler. Finally, it is noted that because of the relatively small area of the flame holder and combustion blower outlet 172, through which the heat exchange tubes 174 are exposed to atmsopheric conditions during the air conditioning cycle of operation of the present invention, there is a minimum cooling loss by natural convection through the boiler during the air conditioning cycle.

Pump 138, used to circulate heat exchange medium from the air conditioning system 10 of the air coil unit located within the house or residence, can be provided in two different embodiments. In one embodiment pump 138 may simply be a centrifugal pump driven by a belt takeoff arrangement (not shown) from the drive shaft of the motor 104. The driven centrifugal pump is used when the system is built to function only as an air conditioner, since in that mode of operation the heat exchange medium is pumped to the house only when motor 104 is operating. (In this form of the invention boiler also is eliminated.) On the other hand, where the system is to be used both as a heating and a cooling system, then pump 38 is provided as a separately powered electric pump since it must operate when boiler 160 is operating to heat the heat exchange medium. Of course, in the heating mode of operation motor 104 is not operating.

Of course, it is to be understood that various ignition and safety controls may be provided in the apparatus of the present invention, as may be thermostatic temperature control arrangements. However, the manner of providing such ignition and thermostatic controls is a matter of choice, as they can be selected in any of a variety of manners. as would occur to those skilled in the art. Accordingly. such controls are not described herein in detail. In addition. it is noted that although unit 10 and the various co ponents thereof are shown in detail. the fluid connections between the components are not shown in complete detail as those connections would be apparent to one skilled in the art. particularly in view of the schematic representation thereof in FIG. 2.

Accordingly. it is seen that a relatively simple system is provided for selectively operating the space conditioning system ofthe present invention as an air conditioner or as a heating system. This enables the evaporator to be placed in series with the boiler and water pump, without the loss of cooling capacity in the air conditioning mode of operation of the device. This is an important feature in cost savings in constructing a system which can provide both heating and cooling. since it makes use of the same components in both the heating and cooling cycles. These components include the indoor heat exchanger coil. heat exchange medium piping, water pump, ignition system, gas pressure regulator and chiller tank evaporator tank which, as mentioned above, provides an expansion tank within its inner core 122, during the heating mode of operation, for the heat exchange medium.

It will also be appreciated that the present invention provides a relatively simple and inexpensive air conditioning and/or heating system in a single space conditioner which is of a compact construction utilizing a minimum number of components. Moreover, the space conditioner of the present invention is gas powered so that it has flexibility in providing both heating and cooling in a single compact arrangement, utilizing relatively inexpensive natural gas. Finally, the space conditioning system of the present invention is highly efficientin operation.

Although an illustrative embodiment has been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of this invention.

What is claimed is:

1. In an absorption-type refrigeration system which includes a generator, condenser, absorber and evaporator, and conduit means for circulating heat exchange medium to and from said evaporator, the improvement which comprises, a selectively operable boiler in fluid communication with said conduit means for selectively heating said heat exchange medium, said boiler including a gas fired burner and having flame holder means, means for supplying pressurized gas and air to said flame holder whereby said gas and air produce blue flame combustion on said holder, means defining a heating chamber above said burner and a heat exchange medium heat exchanger mounted in said chamber in fluid communication with said conduit means, said means for supplying pressurized gas and air and said flame holder cooperating with the other structure to prevent the free circulation of air through said chamber when said burner is not operating and thereby prevent said heat exchanger from being exposed to ambient atmospheric conditions when said burner is not operating, and whereby said boiler is adapted to heat said heat exchange medium flowing through said evaporator thereby to form a combined compact selectively operable heating and cooling system.

2. In an absorption type refrigerant system as defined in claim 1 wherein said heat exchange medium heat exchanger comprises a plurality of heat exchange tubes mounted in said heating chamber, with said tubes being mounted in vertically spaced horizontal alignment with each other and being connected in series to each other for fluid flow therebetween, said tubes having the same internal diameter, and each of said tubes having annular heat exchange fins secured to the exterior surface thereof for transferring heat from the products of combustion of said burner to heat exchange medium flowing in said tubes, the fins on said tubes having progressively larger outside diameters from the lowermost tubes to the uppermost, with respect to said flame holder, whereby heat is transferred to said tubes at substantially the same rate.

3. The air conditioning system as defined in claim 2 including a baffle mounted in said boiler between said tubes for deflecting products of combustion about the tubes. said baffle having slots formed therein to permit said products of combustion to flow upwardly in said boiler.

4. In an absorption type refrigerant system as defined in claim 3 said heat exchanger including at least three pairs of heat exchange tubes, with said pairs of tubes being mounted in vertically spaced horizontal alignment with each other and connected in series for fluid flow therebetween.

5..ln an absorption type refrigeration system as defined in claim 4 wherein said flame holder is approximately six inches long and three inches wide, thereby to minimize convection heat losses during the cooling cycle of operation of the refrigeration system.

6. In an absorptiontype refrigeration system as defined in claim 5, pump means for moving said heat exchange medium through said conduit means.

7. In an air conditioning system, the combination of a central, generally cylindrical hollow core, a vertical cylindrical refrigerant vapor generator assembly adapted to receive liquid to be vaporized and being contained within said cylindrical core, gas fuel combustion means disposed within said core beneath said generator for heating liquid therein, a helically wound tubular condenser supported on and surrounding said central core connected in fluid communication with said generator to receive refrigerant vapor therefrom, fan means mounted on said central core above said generator and condenser for producing ambient air flow for cooling refrigerant vapor flowing in said condenser, a tubular refrigerant heat exchanger supported on and surrounding said central core and connected in fluid communication with said condenser for receiving liquid therefrom, an evaporator, and first restriction means providing fluid communication between said refrigerant heat exchanger and said evaporator. whereby cooled refrigerant liquid is supplied to said evaporator for cooling a heat exchange medium flowing therein, said refrigerant heat exchanger receiving vapor from said evaporator countercurrently from liquid flowing therethrough from said condenser. thereby to cool said liquid from said condenser prior to passage thereof through said restriction means; a helically wound tubular absorber supported on and surrounding said central core adjacent said condenser and operatively connected to said refrigerant heat exchanger to receive refrigerant vapor from said evaporator, said refrigerant vapor flowing in said absorber being cooled by ambient air flow produced by said fan means, a helically wound tubular solution heat exchanger supported on and surrounding said central core and connected in fluid communication between said generator and'said absorber for supplying weak refrigerant therein, second fluid flow restriction means located between said solution heat exchanger and said absorber, and solution pump means for pumping refrigerant solution from said absorber and supplying a first portion thereof directly to the upper portion of said generator and a second portion thereof to said solution heat exchanger wherein strong refrigerant solution flows in heat exchange relation to said weak solution. whereby heat is added to said second portion of the strong refrigerant solution prior to passage into said generator, conduit means for circulating heat exchange medium to and from said evaporator, and a selectively operable boiler in fluid communication with said conduit means for selectively heating said heat exchange medium.

8. The air conditioning system as defined in claim 7 wherein said boiler comprises a gas fired burner having flame holder means and means for supplying pressurized gas and air to said flame Iholder whereby said gas and air produce combustion on said holder, said boiler including means defining a heating chamber above said burner and a heat exchange medium heat exchanger mounted in'said combustion chamber in fluid communication with said last mentioned conduit means.

9. The air conditioning system as defined in claim 8 wherein-said heat exchange medium heat exchanger comprises a plurality of heat exchange tubes. mounted in said-heating chamber, with said tubes being mounted in verticallyv spaced horizontal alignment with each other and being-connected in series-to each other for fluid flow therebetween, said tubes having the same internal diameter, and each of said tubes having annular heat, .exchange fins secured to the exterior surface thereof for transferring heat from the products of combustion of said burner to heat exchange medium flowing in said tubes. the fins on said tubes having progressively larger outside diameters from the lowermost tube to theuppermostg, with; respect to said flame holder, wherebyheat is transferred to said tubes at substan.

tially the same rate. I

-10. Theair conditioning system as defined in claim 9 including a baffle mounted in said boiler between said tubes for deflecting products of combustion about the tubes, said baffle having slots formed therein to permit said products of combustion to flow upwardly in said boiler. v l 1 11. An air conditioning system comprising a generally. vertically,ex.tending refrigerant vapor generator adapted to receivestrong refrigerant solution, gas fired combustion means below said generator for heating strong solution contained therein, a heat exchange condenserconnected in fluid communication with said generator for receiving and cooling refrigerant vapor from said generator, a refrigerant heat exchangerconnectedinfluid communicationgwith said condenser for receiving cooled refrigerant liquid therefrom. a heat exchange evaporator, and first restriction means provid ing fluid communication between said refrigerant heat exchanger and said evaporator whereby cooled refrigerant liquid supplied to said evaporator for changer and said absorber for maintaining a pressure differentialtherebetween, and a solution pump means for pumping strong-refrigerant solution from said absorber and supplying afirstportion thereof directly to the upper portion of said generator and a second portion thereof to said solution heat exchanger, wherein said strong refrigerant solution flows in heat exchange relation to said=weak solution whereby heat is added to said second portion of the strong refrigerant solution prior to passage into said-generator, conduit means for circulating heat exchange'medium to and from said evaporator, and a selectively operable boiler connected in fluid communication with saidconduit means for selectively heating said heat exchange medium.

12. The air conditioning system as defined in claim 11 wherein said boilercomprises a gas fired burner having a wire screen flame: holder and means for supplying pressurized gas and air to said flame holder whereby said gas and air produce combustion on said holder, said boilerincluding means defining a heating chamber above said burner and a heat exchange medium heat exchanger mounted in said combustion chamber in fluid communication with said last mentioned conduitmeans.

13. The airconditioning system as defined in claim 12 wherein said heat exchange medium heat exchanger comprises-at least three pairs of heat exchange tubes mounted in said heating chamber, with said pairs of tubes being mounted in vertically spaced horizontal alignment with each other and being connected in'seriesto each other for'fluid flow therebetween. said tubes having-the same internal diameter, and each of said pairs of tubes having annular heat exchange fins secured to the exterior surface thereof for transferring heat from the products of combustion of said burner to heat exchange medium flowing in said tubes, the fins on said pairs or tubes having progressively larger outside diameters from the lowermost pair of tubes to the up permost. with respect to said flame holder. whereby heat is transferred to said tubes at substantially the same rate in each pair of tubes.

14. The air conditioning system as defined in claim 13 including a baffle mounted in said boiler between said tubes for deflecting products of combustion about the tubes, said baffle having slots formed therein to permit said products of combustion to flow upwardly in said boiler. iv 

1. In an absorption-type refrigeration system which includes a generator, condenser, absorber and evaporator, and conduit means for circulating heat exchange medium to and from said evaporator, the improvement which comprises, a selectively operable boiler in fluid communication with said conduit means for selectively heating said heat exchange medium, said boiler including a gas fired burner and having flame holder means, means for supplying pressurized gas and air to said flame holder whereby said gas and air produce blue flame combustion on said holder, means defining a heating chamber above said burner and a heat exchange medium heat exchanger mounted in said chamber in fluid communication with said conduit means, said means for supplying pressurized gas and air and said flame holder cooperating with the other structure to prevent the free circulation of air through said chamber when said burner is not operating and thereby prevent said heat exchanger from being exposed to ambient atmospheric conditions when said burner is not operating, and whereby said boiler is adapted to heat said heat exchange medium flowing through said evaporator thereby to form a combined compact selectively operable heating and cooling system.
 2. In an absorption type refrigerant system as defined in claim 1 wherein said heat exchange medium heat exchanger comprises a plurality of heat exchange tubes mounted in said heating chamber, with said tubes being mounted in vertically spaced horizontal alignment with each other and being connected in series to each other for fluid flow therebetween, said tubes having the same internal diameter, and each of said tubes having annular heat exchange fins secured to the exterior surface thereof for transferring heat from the products of combustion of said burner to heat exchange medium flowing in said tubes, the fins on said tubes having progressively larger outside diameters from the lowermost tubes to the uppermost, with respect to said flame holder, whereby heat is transferred to said tubes at substantially the same rate.
 3. The air conditioning system as defined in claim 2 including a baffle mounted in said boiler between said tubes for deflecting products of combustion about the tubes, said baffle having slots formed therein to permit said products of combustion to flow upwardly in said boiler.
 4. In an absorption type refrigerant system as defined in claim 3 said heat exchanger including at least three pairs of heat exchange tubes, with said pairs of tubes being mounted in vertically spaced horizontal alignment with each other and connected in series for fluid flow therebetween.
 5. In an absorption type refrigeration system as defined in claim 4 wherein said flame holder is approximately six inches long and three inches wide, thereby to minimize convection heat losses during the cooling cycle of operation of the refrigeration system.
 6. In an absorption type refrigeration system as defined in claim 5, pump means for moving said heat exchange medium through said conduit means.
 7. In an air conditioning system, the combination of a central, generally cylindrical hollow core, a vertical cylindrical refrigerant vapor generator assembly adapted to receive liquid to be vaporized and being contained within said cylindrical core, gas fuel combustion means disposed within said core beneath said generator for heating liquid therein, a helically wound tubular condenser supported on and surrounding said central core connected in fluid communication with said generator to receive refrigerant vapor therefrom, fan means mounted on said central core above said generator and condenser for producing ambient air flow for cooling refrigerant vapor flowing in said condenser, a tubular refrigerant heat exchanger suppoRted on and surrounding said central core and connected in fluid communication with said condenser for receiving liquid therefrom, an evaporator, and first restriction means providing fluid communication between said refrigerant heat exchanger and said evaporator, whereby cooled refrigerant liquid is supplied to said evaporator for cooling a heat exchange medium flowing therein, said refrigerant heat exchanger receiving vapor from said evaporator countercurrently from liquid flowing therethrough from said condenser, thereby to cool said liquid from said condenser prior to passage thereof through said restriction means; a helically wound tubular absorber supported on and surrounding said central core adjacent said condenser and operatively connected to said refrigerant heat exchanger to receive refrigerant vapor from said evaporator, said refrigerant vapor flowing in said absorber being cooled by ambient air flow produced by said fan means, a helically wound tubular solution heat exchanger supported on and surrounding said central core and connected in fluid communication between said generator and said absorber for supplying weak refrigerant therein, second fluid flow restriction means located between said solution heat exchanger and said absorber, and solution pump means for pumping refrigerant solution from said absorber and supplying a first portion thereof directly to the upper portion of said generator and a second portion thereof to said solution heat exchanger wherein strong refrigerant solution flows in heat exchange relation to said weak solution, whereby heat is added to said second portion of the strong refrigerant solution prior to passage into said generator, conduit means for circulating heat exchange medium to and from said evaporator, and a selectively operable boiler in fluid communication with said conduit means for selectively heating said heat exchange medium.
 8. The air conditioning system as defined in claim 7 wherein said boiler comprises a gas fired burner having flame holder means and means for supplying pressurized gas and air to said flame holder whereby said gas and air produce combustion on said holder, said boiler including means defining a heating chamber above said burner and a heat exchange medium heat exchanger mounted in said combustion chamber in fluid communication with said last mentioned conduit means.
 9. The air conditioning system as defined in claim 8 wherein said heat exchange medium heat exchanger comprises a plurality of heat exchange tubes mounted in said heating chamber, with said tubes being mounted in vertically spaced horizontal alignment with each other and being connected in series to each other for fluid flow therebetween, said tubes having the same internal diameter, and each of said tubes having annular heat exchange fins secured to the exterior surface thereof for transferring heat from the products of combustion of said burner to heat exchange medium flowing in said tubes, the fins on said tubes having progressively larger outside diameters from the lowermost tube to the uppermost, with respect to said flame holder, whereby heat is transferred to said tubes at substantially the same rate.
 10. The air conditioning system as defined in claim 9 including a baffle mounted in said boiler between said tubes for deflecting products of combustion about the tubes, said baffle having slots formed therein to permit said products of combustion to flow upwardly in said boiler.
 11. An air conditioning system comprising a generally vertically extending refrigerant vapor generator adapted to receive strong refrigerant solution, gas fired combustion means below said generator for heating strong solution contained therein, a heat exchange condenser connected in fluid communication with said generator for receiving and cooling refrigerant vapor from said generator, a refrigerant heat exchanger connected in fluid communication with said condenser for receiving cooled refrigerant liquid therefrom, a heat exchange Evaporator, and first restriction means providing fluid communication between said refrigerant heat exchanger and said evaporator whereby cooled refrigerant liquid is supplied to said evaporator for cooling a heat exchange medium flowing therein, said refrigerant heat exchanger being adapted to receive refrigerant vapor from said evaporator and pass it countercurrently with refrigerant liquid from said condenser prior to passage through said first restriction means, a heat exchanger absorber connected to said refrigerant heat exchanger in fluid communication for receiving and cooling refrigerant vapor therefrom, a solution heat exchanger connected in fluid communication with said generator and said absorber for supplying weak refrigerant solution from said generator to said absorber for absorbing refrigerant vapor therein; second fluid flow restriction means between said solution heat exchanger and said absorber for maintaining a pressure differential therebetween, and a solution pump means for pumping strong refrigerant solution from said absorber and supplying a first portion thereof directly to the upper portion of said generator and a second portion thereof to said solution heat exchanger, wherein said strong refrigerant solution flows in heat exchange relation to said weak solution whereby heat is added to said second portion of the strong refrigerant solution prior to passage into said generator, conduit means for circulating heat exchange medium to and from said evaporator, and a selectively operable boiler connected in fluid communication with said conduit means for selectively heating said heat exchange medium.
 12. The air conditioning system as defined in claim 11 wherein said boiler comprises a gas fired burner having a wire screen flame holder and means for supplying pressurized gas and air to said flame holder whereby said gas and air produce combustion on said holder, said boiler including means defining a heating chamber above said burner and a heat exchange medium heat exchanger mounted in said combustion chamber in fluid communication with said last mentioned conduit means.
 13. The air conditioning system as defined in claim 12 wherein said heat exchange medium heat exchanger comprises at least three pairs of heat exchange tubes mounted in said heating chamber, with said pairs of tubes being mounted in vertically spaced horizontal alignment with each other and being connected in series to each other for fluid flow therebetween, said tubes having the same internal diameter, and each of said pairs of tubes having annular heat exchange fins secured to the exterior surface thereof for transferring heat from the products of combustion of said burner to heat exchange medium flowing in said tubes, the fins on said pairs or tubes having progressively larger outside diameters from the lowermost pair of tubes to the uppermost, with respect to said flame holder, whereby heat is transferred to said tubes at substantially the same rate in each pair of tubes.
 14. The air conditioning system as defined in claim 13 including a baffle mounted in said boiler between said tubes for deflecting products of combustion about the tubes, said baffle having slots formed therein to permit said products of combustion to flow upwardly in said boiler. 